I. Field of the Invention
This invention relates to a process and apparatus for continuously casting metal strip. More particularly, the invention relates to the continuous casting of metal, such as aluminum (including aluminum alloys), copper, steel or other metals using one or more moving surfaces in the form of heat conducting belts, rolls, wheels or caterpillar block and in particular are conveniently constituted by a pair of flexible heat-conducting bands or belts, such as metal belts in twin belt casters.
II. Description of the Prior Art
Although the continuous casting of metal strip has been under development for many years, and many improvements have been made (see for example improvements to guiding, stabilizing and cooling in twin belt casting apparatus in U.S. Pat. No. 4,061,177 to Sivilotti), difficulty is still encountered in obtaining finished metal products of high surface quality at economical prices.
A particular problem is that the surface appearance of the cast products is easily degraded due to several factors encountered during the casting process. For example, a parting layer is normally applied to the casting surfaces to permit the cooled product to be separated from the casting surfaces. However, if the parting layer is not applied very uniformly, different areas of the surface of the product may have different appearances. Moreover, after contact with the molten metal, the surfaces of the casting surfaces may become contaminated with detritus from the metal and parting agent, and the presence of such material may affect the appearance of the product.
Surface problems can also be caused as the molten metal is applied to the moving casting surfaces. This is usually achieved by means of an injector that extends over the operating width of the casting surfaces, but problems arise unless the injector is spaced from the moving casting surface by a precise small distance. However, methods of maintaining such a distance without contact with the moving casting surface are not very accurate, are not sufficiently reliable (due to mechanical and thermal distortions which can permit metal flashback for example) and methods using contacts with the moving casting surfaces usually disrupt the layer of parting agent applied to the casting surface or cause premature solidification of the metal in the injector due to heat transfer to the belt.
There is accordingly a need for improvements in such casting processes and apparatus to overcome such defects in the finished products and such unreliability of operation.